1. Field of Invention
The present invention relates to a dual power switch and a voltage regulator employing the dual power switch.
2. Description of Related Art
Voltage regulators include linear regulators, buck converters, boost converters, buck-boost converters, inverter converters, fly-back converters, AC-DC converters, and the like. All these regulators must employ one or more power switches. In general, as shown in FIGS. 1 and 2, such power switch is either a PMOS transistor (device 10 in FIG. 1) or an NMOS transistor device 20 in FIG. 2). When the power switch 10 or 20 is ON, current flows from the input terminal Vin to the output terminal Vout (depending on the structure of the voltage regulator, the output terminal Vout in the figures does not necessarily correspond to the output terminal of a regulator which supplies power to a load; in the context of this specification, the terminals Vin and Vout represent both sides of the power switch). The operation of the power switch 10 or 20 is controlled by a control circuit 15 or 25. In some applications, because the NMOS transistor 20 requires a higher gate voltage, a charge pump 23 may be required to pump up the voltage for the control circuit 25.
The above mentioned prior art has the drawback that the resistance of a PMOS power switch in ON state is high, while the power consumption of an NMOS power switch is high. A circuit designer has to choose one between the two, but can not gain both.
In view of the foregoing, it is desired to provide a dual power switch.